Following rP26879, we can actually parse the autostart arguments in Javascript instead of C++.
This makes it easier for modders to support their own settings, and is generally rather easier to write, particularly since we can rely on the GameSettings abstraction.
Further work:
- It's rather easy to extend autostart to other things, should we want to.
Relates to #3049 (general gamesetup cleanup ticket), #5075 (this removes the GameSetup.cpp case, the readme is an open question), #3438 (invalidated).